The libertarian-leaning senator, who's a potential 2016 Republican presidential candidate, said he thought the September 11, 2012, attack in Benghazi, Libya, where four American diplomats were killed, was a "failure of leadership."

"If I were president at the time I would've relieved you of your post," Paul said.

The attack was initially reported by UN Ambassador Susan Rice as the result of a "spontaneous demonstration." However, intelligence available at the time described the attacks as planned and executed by an al-Qaeda affiliate.